1. Field of the Invention
The present invention relates to a mold device having a combination of molds for stretch blow molding, comprising a main blow cavity, which is for molding a container such as a plastic bottle, and a pre-blow mold below, and pre-blow molding and main blow molding are operated at a same position.
2. Background Art
A conventional art discloses a mold device having a combination of molds which uses a pair of split pre-blow molds, which can be opened and closed on a bed by a mold clamping device, and a pair of main blow molds, placed under the pre-blow molds which is movable upward and downward, and the main blow molds can be clamped with the pre-blow molds by the clamping device (reference patent: U.S. Pat. No. 5,635,226).
The conventional device disclosed in U.S. Pat. No. 5,635,226 uses a pair of split molds for a pre-blow mold, so that a parting line is left on a preliminary article formed in pre-blow molding, and also another parting line is marked on the same location by main blow molds. Consequently, the longitudinal convex parting line becomes more exaggerated than a parting line on a bottle, which doesn't require pre-blow molding, so it often affects the appearance of the bottle or causes a problem for labeling.
Moreover, because the pre-blow molds and the main blow molds share a common clamping device to be closed, the number of clamping operation increases comparing to the clamping process in blow molding without pre-blow molding. The stroke of the pre-blow molds is set longer in order to insert the main blow molds between the pre-blow mold halves at opening state, and as an evitable result, the length of a ram for the mold clamping device has to be long. It takes a long time to open or close the main blow molds, and it causes a delay in the molding cycle time including the increase of the number of clamping action.
Furthermore, since the main blow molds are clamped with the pre-blow molds, the pre-blow molds have to be as large as the main blow molds irrelevantly to the substantial requirement for the pre-blow molding even in the pre-blow molding process wherein the preform is stretch blow molded by a little because the pre-blow molds have to be able to press the whole main blow molds. Besides, the main blow molds can't be opened by itself, so it requires an apparatus for opening the main blow mold with the backward movement of the mold clamping device. Consequently, the blow molding device tends to be complicated and large.
The problem of the blow mold device mentioned above can't be solved by changing the position of the molds by placing the main blow molds on the bed and the pre-blow molds under the main blow molds as long as a pair of split molds is adopted for the pre-blow molds. Also, if the pre-blow molds are movable between the split main blow mold halves, it is difficult to place a bottom mold for the main blow mold, and the usage of the main blow mold is limited to a mold for a container having a flat bottom, which is removable with the opening by the main blow mold.